1. Field of the Invention
This invention relates to a new process for preparing acetaldehyde. More particularly, the invention relates to a new process for preparing acetaldehyde from methanol and synthesis gas using a novel catalyst composition.
Specifically, the invention provides a new and improved process for preparing acetaldehyde from methanol and syngas in good yield under mild reaction conditions, which process comprises contacting a mixture of methanol, carbon monoxide and hydrogen with an iodide or iodine free catalyst composition comprising (1) ruthenium powder, (2) a cobalt-containing compound, (3) a rhodium-containing compound, and (4) an onium salt or base, and heating the resulting mixture under mild temperature and pressure for sufficient time to produce the desired acetaldehyde, and then recovering the same from the reaction mixture.
2. Prior Art
Acetaldehyde is an important chemical of commerce used in a great variety of applications, such as, for example, in the preparation of acetic acid, vinyl acetate, chloral, cyanohydrins and polyhydric alcohol derivatives, such as the glycol monoalkyl ethers. Acetaldehyde has been produced heretofore by methods, such as the hydration of acetylene or the oxidation of ethylene. Such methods, however, have their limitations, particularly as to cost, and it would be desirable to find a more economical method for producing this compound.
U.S. Pat. No. 4,151,208 discloses a method for producing acetaldehyde from methanol and syngas using a catalyst comprising a special cobalt compound and an iodine promoter. This process is limited, however, because of the serious corrosion problems due to the presence of the iodine promoter. U.S. Pat. No. 4,201,868 discloses a process for preparing a mixture of products containing acetaldehyde using a catalyst comprising a cobalt carbonyl and an organic nitrogen-containing ligand. This process, however, is limited by its poor selectivity.
It is an object of the invention, therefore, to provide a new and improved process for preparing acetaldehyde. It is a further object to provide a process for preparing acetaldehyde from methanol and syngas using a new and improved catalyst system. It is a further object to provide a new process for preparing acetaldehyde from methanol and syngas which gives good selectivity and yield of the desired product. It is a further object to provide a process for preparing acetaldehyde from methanol and syngas which utilizes milder reaction conditions, particularly as to the use of lower pressures and temperatures, than used heretofore. It is a further object to provide a process for preparing acetaldehyde which utilizes a catalyst free of corrosive elements and is capable of being used on a large commercial scale. These and other objects of the invention will be apparent from the following detailed description thereof.